Problem is to provide a bone conduction speaker unit which is compact as a whole, and can be used, being simply and neatly mounted to a great variety of pieces of existing communication equipment, such as mobile phones. A unit case 1 is provided which incorporates a bone conduction speaker 2 such that a diaphragm 3 is exposed, with an earphone-jack mating plug 4, which is connected to the bone conduction speaker 2, being disposed on the unit case 1, and by connecting the plug 4 to an earphone jack 22 on a cabinet 21 of a piece of communication equipment, such as a mobile phone, the piece of communication equipment is allowed to be used as a speaker.